Protection of cellulose fiber against heat aging and tire casing containing such fiber



Jan. 12, 1954 H. M. BUCKWALTER PROTECTION OF CELLU LOSE FIBER AGAINST HEAT AGING AND TIRE CASING CONTAINING SUCH FIBER Filed Feb. 27, 1951 70 PREVE/VTHEAT DTE/F/OFAT/O/V Patented Jan. 12, 1954 PROTECTION OF CELLULOSE FIBER AGAINST HEAT AGING AND TIRE CASING CONTAINING SUCH FIBER Howard M. Buckwalter, Detroit, Mich., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey Application February 27, 1951, Serial No. 213,040

7 Claims. 1

This invention relates to the protection of native and regenerated cellulose fibers against deterioration by heat aging. This application is a continuation-in-part of my application Serial No. 116,856, filed September 20, 1949, and now abandoned.

Deterioration of cellulose fiber upon subjection to elevated temperatures for prolonged periods of time is a very serious problem in the art. This problem is encountered particularly in the case of rubber articles which are reinjforced with cellulose'fiber, almost invariably stranded and in the form of cords or fabric, which may be a woven fabric having warp and woof threads or a so-called weftless fabric or web fabric composed of parallel cords joined together by a dry deposit of rubber latex, as described for example in the patent to Hopkinson, No. 1,424,020. Such cellulose fiber reinforced articles include pneumatic tires, steam hose, power transmission belts, conveyor belts, etc. These articles are subjected to elevated temperatures in normal use, either because they are subjected to external heating, or because they generate heat within themselves by reason of repeated rapid flexing, as in the case of pneumatic tires. The deterioration of the reinforcing cellulose fiber under the action of heat is particularly evidenced by progressive reduction in tensile strength of the fiber, leading to eventual breakage. This deteriorating action of prolonged heating on cellulose fibers is a principal cause of failure of such articles as pneumatic tires and steam hose.

The principal object of the present invention as is to provide an improved method of protecting cellulose fiber, especially when stranded and in the form of a fabric, against deterioration by heat aging. Another object is to provide articles of manufacture embodying cellulose fibers protected against heat deterioration, such articles of manufacture including cellulose fibers themselves, whether unstranded, stranded, or in the form of fabric, and vulcanized rubber articles reinforced with such cellulose fibers, such as pneumatic tire casings reinforced therewith. Other objects of the invention will more fully hereinafter appear. The single figure of the accompanying drawing is a transverse sectionalview of a pneumatic tire reinforced with cellulosic tire cords treated inaccordance with the invention. The structure of the tire is otherwise conventional.

According to the present invention, cellulose fiber is protected against deterioration by heat aging by incorporating dicyandiamide therein. I have found that dicyandiamide is a remarkably effective chemical in imparting to cellulose fibers the ability to withstand deterioration by the action of heat over extended periods of time.

In carrying out the invention, the dicyandiamide may be applied to the cellulose fiber in any suitable manner, conveniently by immersing the fiber to be treated in a solution of the dicyandiamide for a time sufficient for the fiber to become substantially impregnated with the dicyandiamide solution. Another method of incorporating the dicyandiamide in the cellulose fiber is to form the dicyandiamide fin situ within the fiber, that is, the fiber may be first treated at room temperatures with cyanamide solution. (pH 6-10) in any suitable manner, and subsequently subjected to conditions which will cause the cyanamide to be dimerized to dicyandiamide, g., slow dimerization on prolonged standing at room temperature, or more rapid dimerizaticn during drying of the fabric at elevated temperatures (l50-200 F.) or during curing (250-290 F.) when the product is incorporated in rubber.

The cellulose fiber employed is usually ordinary grey cotton fiber although the process of the invention may also be employed advantageously with the various regenerated cellulose fibers, such as viscose rayon. The invention is applicable to native cellulose fibers in general, such as flax, hemp, etc., as well as to scoured, bleached and mercerized cotton. In place of immersing the fiber in the treating solution, I may incorporate the dicyandiamide or cyanamide in the fiber in any other suitable manner, such as by spraying or brushing.

For convenience, I usually employ the dicyandiamide in the form of an aqueous solution, typically at a concentration of 10% by weight, although marked improvement in heat age resistance is also obtainable with surprisingly dilute solutions, e, g., solutions containing 0.2% dicyandiamide. If desired, more concentrated solutions may be employed, e. g., a 20% soluticn, or even a saturated solution (46% at 100 C.) although there is ordinarily only minor ad:- vantage in using solutions more concentrated than about 25%. cyanamide in solution may be used in place of dicyandiamide, provided the temperature does not exceed average room temperatures to avoid as far as possible spontaneous polymerization, andlater dimerized.

The treatment with dicyandiamide may be carried out at room temperature, or at elevated temperatures, for example, up to the boiling point of the aqueous solution. The time of contact between the cellulose fiber and the treating solution should be sufficient to permit substantial penetration of the fiber. Usually treatment times of from 15 seconds to IO-minutesat the boiling point are adequate for this purpose; although; longer. treatment times are without adverse efiect and may be employed if desired.

In order to obtain the benefits of the treatment of this invention it is necessary;thatitheidicyandie amide remain in the cellulose fibe'r.and:be actually present as such in the fiber at the time the fiber is subjected to the heating: which; would 4 untreated cord after subjecting to the heat deterioration conditions.

EXAMPLE 2 Grey cotton tire cord and-.viscoserayon tire cord weret-reated with aqueousrdicyandiamide solutions-of varying concentration for two minutes at: the boiling point of the solution in the same manner as in Example 1. The cords were similarly'drained, dried, and subjected to open heat agingconditions; and tested for tensile strength in the manner previously indicated. The results are shown inTableL.

Table I O PEN.HEA'I..AGING,.OE COTTON AND RAYON CORD Cotton Rayon W h d d Hours eig tpercent ioyan iopen amidein treating solu. heat? Percent agitig at 553 1251 origi nal' Relative s tgi r l g t h origi nal Relative 165 1bs.,v strength strength lbs. strength strength retained retained" 0" 16. 6 100' 21.0 100 72 (i. 4 39 100 8. 5 40 100 72v 11.1 67 173 9.1 43v 107 72 11. O 66 172 9; 0 43' 106 72 11; 7' 70. 183' 9. 2 44 108' 72. 11.3 68. 176 9. 3 44 109 72 13. 0 79 203' 9; 3 44 109' 72" 14-. 5; 87 226 10.3, 49. 121. 72. 14.9 90 232 11.1) 52 129. 72 15:2 91 237 11. 6 55 136 ordinarily 'causedeterioration. I have found that dicyandiamide. present. in. the cellulose fiber in amountirom 0:1; to 10.0% orrthe. weight of,.the fiber is effective to produce substantialimprove,- ment in the heat age resistanceof the fiber.

The following examples will :illustrate; the. practice of my invention in more detail.

EXAMPLE 1 chemical deterioration ofthe cotton by; the;acti0nofgthe'heat', namely 12.5? 0.3 After such aging the tensile strength ofthe; treated cotton cord was determinedat 70. F, and ;60% relative humidity,

andthe results obtained-werecompared to con trolsamples as follows:

T 3 Percent 101 I I ens e Ollgll'lfl Relative 7 Sample strelngg'th, s tergggh strength,

ing

Control; untreated, unaged 16. 6 100 Control; untreated, aged 6; 4 39 100 Dicyandiamide treated, aged "-1 13; 2 80 206 The-foregoingdata shows that while the -untreated cottoncord retained only 39 of itsoriginal strength after' the 'openheat aging; the dicyandiamide treated-cord retained 80% of its-- original strength. The dicyandiamidetreated The-data in Table 1' indicate that dicyandiamide; at .all. concentrations has amuch 1 greater heatstabilizing efiect on greyv cottonthan it has onfrayon.v For example, a;20%j solution of dicyan-= diamide-increased, the'72. hour 165 C. agestrength of cotton..13'7%,,whereas rayomunderi oomparablezconditions, isimprovedonly 361%,.

EXAMPLE 3 Grey, cotton tire :cord was treated with aqueous dicyandiamide of various concentrations in the Samema-nner as in theforegoing examples The treated cord wasconditioned 24hoursat70 F relative humidity and then .sealed ina tube. and'subjected .to heataging for 72 hours at.165. C., followingzwhich .thetube. was broken and the-aged= cordwastensile tested at F. and'60 relative. humidity, The. data. obtained are tabulated in. IableIIl TableJI.

SEALED TUBE AGING OF COTTUN "CQ RD- Hts; aged- Percent of" Weight percent Dicyandia in sealed gg' original mide in treating sol'ution tube at fg strength 1 165 0. i retained These data indicate that dicyandiamide also affords excellent protection against pyrolysis, or heat deterioration, under sealed aging conditions. Such sealed l'ieat aging-tests'are found to correlate closely with the behavior'of" the cellulose fiber: under service conditions wherein the fiber is substantially isolated from the influence of the ambient atmosphere; such-as in pneumatic tires; where I the-- fibers are encased inlayers of cord. was more than-two-times as strong'as the substantially: impervious: rubber.

' I have also found that it is advantageous to combine the dicyandiamide treatment of the present invention with the treatment of cotton fibers with sodium rosinate-silicate and the like, as described in my U. S. Patent 2,297,536 issued September 29, 1942. The sodium rosinate-silicate treatment protects the grey cotton against the temporary reversible loss of tensile strength which normally occurs substantially instantaneously upon heating the cotton to elevated temperature, while the dicyandiamide protects against the progressive, irreversible loss of strength which occurs upon extended exposure to heat. In this form of the invention the two treatments can be carried out simultaneously by adding the dicyandiamide to the sodium rosinatesilicate solution, or the treatments may be carried out successively in any desired order. If desired, the treated cord may be stretched, or stretched and shrunk, to effect further increase in tensile strength. The following example illustrates a combined treatment with dicyandiamide and sodium rosinate-silicate.

EXAMPLE 4 Table III COMBINED TREATMENT OF COTTON W ITH DIOYANDIAMIDE AND SODIUM ROSINATE Weight Weight percent percent dicyan- Hrs. Tensile Percent of aqueous diamide open, stren m original Relative sodiumadded to aging at g strength strength resinate sodium- 165 0. retained solution rosinate solution The data of Table III indicate that dicyandiamide also produces substantial improvement in resistance to heat aging in cotton cord treated with sodium rosinate solution.

EXAIMPLE 5 This example illustrates formation of dycyandiamide in situ in tire cord by treating the cord with a composition of cyanamide. The example also illustrates combination of the treatment according to the invention with a rubber latex impregnating step, which is a conventional step in preparing pneumatic tire fabric for incorporation in the tire carcass.

Rayon tire cord was impregnated with rubber latex containing varying concentrations of cyanamide, as indicated in Table IV below. The cord was treated by immersing it for three sec onds at room temperature in a latex-resin composition containing, in addition, to cyanamide in amounts shown, GR-S or natural rubber latex compounded with the conventional curatives and-modifiers, e. g., sulfur, zinc oxide, accelerator and resorcinol resin. The treated cord was dried for 15 minutes at 220 F. It is believed that the cyanamide began to dimerize to some extent in the latex bath, and that the heat of the drying operation brought the dimerization substantially to completion.

The cord fabric was then skim coated with vulcanizable rubber tire carcassstock in the usual manner, and fabricated into 4.008 size 6 ply pneumatic tires which were vulcanized by the usual factory methods. The tires were mounted on test wheels and inflated, and subjected to a temperature of 392 F. for 72 hours to test the ability of the cords to resist high-temperature degradation. After this aging period, the cords were removed from the tires and the tensile strength of the cords was measured at 70 F. and 60% relative humidity, with the results noted in Table IV.

Table IV Tensile strength of cord Concentration of cyanamide H ms a d (parts by weight in 8 0 parts of latex) Lbs Relative strength None 0 21.0 None 72 6.3 100 5.. 72 12.0 191 72 14. 5 230 72 14. 9 236 72 l6. 4 260 72 16.6 263 Inspection of the foregoing data will reveal that the cyanamide treatment imparted to the tire cords an improved ability to withstand within the tire the deteriorating effects of prolonged exposure to elevated temperatures.

EXAMPLE 6 The foregoing Example 5 was repeated, except that dicyandiamide was used in the latex composition in place of cyanamide. Tires made with the treated cord were aged on a test wheel as before, with the results shown in Table V:

Table V Concentration of dicyandi- Tensile strength of cord amide in latex (parts by weight per 100 perts of latex) Tire aged at 0., 3

hours 1 Relative I strength It is evident from the data of Table V that the cord containing dicyandiamide withstood heat deterioration in the tire to a marked degree.

From the foregoing it is evident that the invention provides a method of treating cellulose fibers, whether grey cotton fibers or other forms of cellulose fiber such as regenerated cellulose, whether in the form of fibers as such, or as yarn, cord or fabric, whereby the resistance of the fiber to the deteriorating effect of prolonged exposure to elevated temperature is substantially enhancedj Thus, the improved cellulose fibers of this invention containing dicyandiamide are capable of improved serviceability especially when employed for such purposes as reinforcing tires, steam hose, and similar rubber-composite arti '-c1'cs-:which normally have a limited servicelife because of the deteriorating action of beat on the fiber reinforcement therein.

The dicyandiamide treated fiber can be en cased in rubber which may be subsequently vulcanized at elevated temperatures to a dense, strong product without any adverse effects due to the-presence of the dicyandiamide. This is in contrast to certain other chemicals previously proposed for improving theheat age resistance of. rayon cords andthe like, but which are imipractical because they decompose at vulcanizing' temperatures with liberation of gases, causing blowing in the carcass assembly. Because the dicyandiamide is comparatively stable at vulcanmust actually remain as such in the cellulose fiber and be present while the fiber is expos edto elevated temperature service conditions in order to obtainthe beneficial efiects of the treatment. .1

In this respect, my treatment difiers from cer tain conventional treatments, particularly treatments designed to obviate the temporary, reversible loss of strength observed in grey cottonfibers when heated at elevated temperatures; temporary loss of tensile strength occurs substanti-ally instantaneously upon heating to elevated temperature, and the cotton regains its original strength upon cooling to room temperature. Such temporary reversible loss of tensile strength at elevated temperature is obviated in the prior art methods referred to by removing the waxes from the native cotton; and suchtreatments are characterized by the fact that it is immaterial whether the treating agent is' eventually removed from thecotton or whether the treating agent remains in. the cotton. In contrast to this, the present invention is concerned with the irreversible chemical changes: which occur in cellulosic fibers, whether grey cotton con- I Such taming natural waxes, or dewaxed cotton, or re- The foregoing considerations also apply when the dicyandiamide is prepared "in situ, that is when cyanamide is applied to the fiber and later converted to dicyandiamide. The cyanamide must not be washed out, or changed in. chemical identity before it is dimerized to dicyandiamide. While I have described my invention with par ticular reference to a. preferred treatment of cellulose fibers intended to be. used for reiniorcing rubber articles, it will be. understood that, the improvedv dicyand'iamid'e containing. cellulose preferably in fibers of this invention" are Jsusc'eptible'of: many other'uses where resistance to heat a desirable characteristic. However, the improved cellulose fibers of the invention are especially adapted to production of vulcanized rubber-fabric composite articles, because the dicyandiamide or cyanamide have no deleterious efiect on the vulcanization, and the dicyandiamide resists vulcanizing' ternperatures, thereby resulting in. improved vulcanized. rubbersilablic composite articles;

It will be understood that-the reierencesherei'n to preservation ottlie fibers from heat deteriora. tion. are notintended to indicate that the treated fibers are flame resistant or fireproof, andtherefore. no claim is made that the invention is capa ble of. preventing rapid oxidationand consequent deterioration of the cellulose when it is exposed to temperatures above its.- ignitiontemperature.

Having thus described my invention what I claim and desire to: protect-by Letters Patent is:

1- The" method of, improving the'resistance of cellulose fibers to they deteriorating. eficcts of heat aging which comprises. incorporating dicyandiamide in the cellulose fiber in amount of from 0.1 to 10.0% by weight and preserving the dicyandiamide as suchin the fibersrwhereby the said dicyandiamide preserved inthe fibers is available as such during subsequent exposure of thethus treated fibers to heat aging andthe fibers are thereby substantially preserved against permanent irreversible lossof their original strength level after prolonged exposure to temperatures above l25 C. but below the ignition temperature of the fibers.

2. The method of improving the resistance of cellulose fibers to the deteriorating effects of heat aging which comprises impregnating the fibers with an aqueous solution containing from 0.2% to 25 by Weight of dicyandiamide and preserving the dicyandiamide as. such in the fibers whereby the: said d-icyandiamide preserved'in the fibers is available as such during subsequent exposure of the thus treated fibersto heat aging and the fibers are thereby substantially preserved against permanent, irreversible loss of their original strength level after prolonged exposure to temperatures above 125 C. but below the ignition temperature of the fibers.

3. The method of improving; the resistance of regenerated cellulose fibers to the deteriorating efiect of heat aging which comprises impregnating the: regenerated cellulose fibers withran aque ous solution containing from 0.2 to 25% by weight of dicyandiamide and preserving the dicyandiamide as such. in the fibers whereby the said dicyandiamide preserved in the fibers is available as such during subsequent exposure of the thus treated fibers to heat aging and the fibers are thereby substantially preserved against permanent, irreversible loss of their originalstrength level after prolonged. exposure to. temperatures above 125 C. but below the ignition temperature of the fibers.

4. The method of improving the resistance of cellulose fibers to the deteriorating. efiects of heat aging which comprises incorporating cyanamide in the cellulose fiber. in amount of; from 0.1 to 10.0% by weight; subjecting the cyanami'd'e to a temperature suiiicien'tlyv elevated to convert it to dicyand'iamide and preserving. the dicyandiamide as such in the fibers. whereby the said dicyandiamide is available assuch during subsequent exposure of the thus treated fibers to heat. aging and the fibers are thereby substantially preserved against permanent, irreversible loss of. their References Cited in the file of this patent UNITED STATES PATENTS Name Date Lessig et al. Nov. 18, 1941 Number Number Name Date 2,278,284 Reese Mar. 31, 1942 2,380,157 Dreyfus July 10, 1945 ,446 Buckwalter et a1. Sept. 5, 1950 2,524,783 Ford et a1. Oct. 10, 1950 2,539,558 Studeny et a1. Jan. 30, 1951 FOREIGN PATENTS Number Country Date 432,927 Italy Mar. 30, 1948 OTHER REFERENCES "American Dyestuif Reporter" of January 12, 1948, pages 10-15. 

4. THE METHOD OF IMPROVING THE RESISTANCE OF CELLULOSE FIBERS TO THE DETERIORATING EFFECTS OF HEAT AGING WHICH COMPRISES INCORPORATING CYANAMIDE IN THE CELLULOSE FIBER IN AMOUNT OF FROM 0.1 TO 10.0% BY WEIGHT, SUBJECTING THE CYANAMIDE TO A TEMPERATURE SUFFICIENTLY ELEVATED TO CONVERT IT TO DICYANDIAMIDE AND PRESERVING THE DICYANDIAMIDE AS SUCH IN THE FIBERS WHEREBY THE SAID DICYANDIAMIDE IS AVAILABLE AS SUCH DURING SUBSEQUENT EXPOSURE OF THE THUS TREATED FIBERS TO HEAT AGING AND THE FIBERS ARE THEREBY SUBSTANTIALLY PRESERVED AGAINST PERMANENT, IRREVERSIBLE LOSS OF THEIR ORIGINAL STRENGTH LEVEL AFTER EXPOSURE TO TEMPERATURES ABOVE 125* C. BUT BELOW THE IGNITION TEMPERATURE OF THE FIBERS. 